1. Field of the Invention
This invention relates to a zoom lens system, and in particular to a zoom lens system for use in a television camera, a video camera, a still camara or the like which utilizes an element whose radius of curvature is variable and which is compact and can obtain a high magnification change ratio.
2. Related Background Art
In zoom lenses, the requirements for compactness and high magnification change ratio have been great, and to satisfy these requirements, there are known the self-contained extender systems as shown in Japanese Pat. Publications Nos. 7606/1986 and 40965/1986. However, these are of the change-over magnification change type and therefore, high mechanical accuracy is required for the securement of the lens containing space and the adjustment of the optic axis, and further, since they are incapable of continuous magnification change, they have suffered from the disadvantage that they cannot be used in the other cases than the changeover of the scene to be photographed or the F-value becomes as great as that at the telephoto end from the intermediate focal length position.
As another means, there is known a zoom lens system in which two zoom portions movable on the optic axis are provided in a photo-taking lens, as seen in Japanese Pat. Publication No. 4461/1977 (U.S. Pat. No. 4,033,674). However, this system has suffered from the disadvantage that particularly the second zoom portion provided on the image surface side, as compared with the ordinary relay portion, results in the complication of the lens construction for the reasons such as the securement of the space for movement and the correction of aberrations and the full length becomes greater.
As the related art, there are the systems disclosed in U.S. Applications Ser. No. 737,342 now U.S. Pat. No. 4,784,479, No. 556,705, No. 813,227 now U.S. Pat. No. 4,820,028, and U.S. Pat. No. 4,407,567, No. 4,678,899.